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This paper describes in detail the measurement of the overall heat transfer coefficient and phase transformation latent heat by modified pattern search method (PSM). By introducing the pattern search algorithm into finite element analysis, the measurement of heat transfer coefficients and phase transformation latent heat can be simplified as recording the temperature with time. Comparison of the measurements by PSM and temperature gradient method (TGM) shows that PSM can evaluate the overall heat transfer coefficient accurately. Experiments and simulations show that bainite transformation latent heat in 26NiCrMoV10-10 steel is about − 90.5 J/g, and the latent heat increases the surface temperature of a cylindrical specimen by a maximum of 76 °C. Error analysis shows that the highest difference between calculated temperature and measured temperature is 11.7 °C, which verifies that the heat transfer coefficient and phase transformation latent heat estimated by PSM are accurate, and that the pattern search method is reliable. [ABSTRACT FROM AUTHOR]

In this paper, the melting and solidification processes and the thermal conductivity enhancement of the phase change material (PCM) inside a sphere have been experimentally investigated to facilitate a greater understanding and improvement of the phase change heat transfer of PCM inside a sphere. The experiments are conducted by inserting a sphere filled with organic PCM into a constant temperature bath of hot/cold water. Through measuring and analyzing the temperature field inside the sphere under conditions of various initial and final temperatures, the thermal characteristics of melting and solidification processes of PCM are obtained. To determine the thermal conductivity enhancement effect of aluminum powder, the PCM-aluminum composite material in which the mass fractions of aluminum are 1% and 2%, respectively, is tested. And the experimental data of PCM-aluminum composite material are compared with those of pure PCM. Results indicate that the PCM in the upper part of the sphere melts faster than that in the lower part, and the PCM near the inner wall solidifies faster than that in the center of the sphere. The initial PCM temperature has little effect on the solidification process of the PCM inside the sphere when Stefan number ( Ste ) is small and Rayleigh number ( Ra ) is large. The thermal conductivity of the PCM inside the sphere is enhanced by adding aluminum powder. And the sedimentation of aluminum powder is more beneficial to accelerate the heat transfer of the whole sphere in the melting process, compared with the uniform diffusion of aluminum powder in the PCM. [ABSTRACT FROM AUTHOR]

In this paper, laminar forced convective heat transfer of water/alumina nanofluids in a straight microchannel is studied numerically using CFD modeling. In the first part, single-phase and two-phase mixture models have been used for prediction of hydrodynamics and heat transfer parameters of nanofluids in a simple microchannel heat sink. The CFD predictions were compared to the experimental data and it was concluded that the two-phase approach gives better predictions compared to the single-phase model. The effects of ribs turbulators on the fluid flow and heat transfer performance of microchannel were investigated in the second part. The effects of geometrical characteristics of the ribs were studied, and the results showed that the Nusselt number and friction coefficient of nanofluids in the ribbed microchannel are higher than those of simple microchannel, and this enhancement increased with increasing the width of the ribs. [ABSTRACT FROM AUTHOR]

Based on constructal theory, the construct of a three-dimensional cylindrical heat sources with convection heat transfer is investigated in this paper. The heat source model is composed of several cylindrical heat sources surrounded with a cylindrical fin or a conical fin. The heat source model not only exists in the heat generating electronic component surrounded with a fin to enhance heat transfer, but also in the heat generating fuel rod with zircaloy cladding. For the specified volumes of the fin and the heat sources, this construct is optimized by taking the minimization of the dimensionless hot spot temperature as optimization objective. The results show that the hot spot temperature of the model is effectively reduced after constructal optimization, which will provider some theoretical guidelines for the optimal design of heat source system. [ABSTRACT FROM AUTHOR]

In this paper, the characteristic variational multiscale (C-VMS) method is proposed to solve the nonstationary conduction–convection problems. The stability analysis is carried out using the energy estimate method. Compared with the standard variational multiscale (VMS) method, the C-VMS method does not need nonlinear iteration. Finally, some numerical examples are given, which show that the C-VMS method is efficient, reliable and can save a lot of CPU time for this problem, besides, it can deal with the high Rayleigh number. [ABSTRACT FROM AUTHOR]

This paper reviewed the application of nanofluids in vehicle engine cooling system. So far, nanoparticles have been used in engine oil, transmission oil, and radiator coolant to enhance heat transfer removal from vehicle engine. The heat transfer performance of nanofluids has been reported to perform better compared to pure fluid. This review focused on the experimental and numerical studies by previous researchers and their suggested amount of nanoparticles for optimum performance in vehicle engine cooling system. Finally, the conclusions and important summaries were presented according to the data collected. [ABSTRACT FROM AUTHOR]

This paper provides a review about the major work done on helical baffles to improve the performance of shell and tube heat exchangers. Some of the major factors affecting the performance of shell and tube heat exchanger are discussed. A comparison between segmental baffles and helical baffles is also presented to show that helical baffles are more advantageous than segmental baffles. In most cases, discontinuous, folded, sextant helical baffles, 40° baffle inclination angle as well as low baffle spacing will give the best results when integrated in some combination, whereas continuous helical baffles eliminate dead regions. Moreover, sealing strips are more likely to improve the performance of shell and tube heat exchangers with continuous helical baffles. [ABSTRACT FROM AUTHOR]

In this paper, heat transfer characteristics and flow visualization of the hydrocarbon refrigerant R-600a during flow boiling inside horizontal smooth tube are investigated. For this purpose the well instrumented experimental apparatus including pump, flow meter, pre-heaters, test evaporator, by-pass and condenser was designed, fabricated and installed in order to measure the experimental data on flow boiling heat transfer and flow pattern of hydrocarbon refrigerant. The test section was a plain copper tube with an inside diameter of 8.7 mm and a wall thickness of 0.41 mm. The experimental tests were carried out varying: (i) the refrigerant mass fluxes within the range of 130–380 kg/m 2 s; (ii) the vapor qualities up to 0.70; and (iii) the heat fluxes from 10 to 27 kW/m 2 . The results indicate that, intermittent and annular flow patterns are the dominant flow patterns in the ranges of operating parameters of the present study. Also, the flow boiling heat transfer coefficient increased as the mass velocity increased in the fixed vapor quality. Moreover, heat transfer coefficient increased by the increase of vapor quality as the mass velocity was fixed. Most of the flow boiling heat transfer and flow pattern prediction methods have been developed for HFC and HCFC and CFC refrigerants and there are no general methods which can be applicable for all fluids. Therefore the present study experimental data for flow boiling heat transfer coefficient and flow pattern were compared with some existing models in order to find out which method could predict the convective boiling heat transfer and flow pattern characteristics of R-600a as a hydrocarbon refrigerant more accurately. The results indicate that Kattan–Thome–Favrat [23] flow map was closer to the flow patterns observed in this study. In addition, Gungor–Winterton [8] correlation had the best consistency with the present study experimental heat transfer data. [ABSTRACT FROM AUTHOR]

In this paper, natural convection heat transfer and fluid flow within a single slope solar still (SSSS) are investigated numerically. To enhance the productivity and performance of this system, the differences of bladed and non-bladed solar stills in terms of vortices resulted from natural convection heat transfer are presented. It is assumed that the flow within the still is two-dimensional, steady and laminar. The numerical method is based on SIMPLEC algorithm and is used for discretization and solving continuity, momentum, energy and concentration conservation equations. The blades are installed on the non-insulated walls of solar stills in two different ways; downward and upward. Results are posed for different blade locations, Rayleigh and Nusselt numbers. Moreover, results depict that exploiting a blade can augment system's performance substantially in comparison with more than one. Comparison of the present numerical approach and well-known published empirical correlations proves the acceptable accuracy of this study. [ABSTRACT FROM AUTHOR]

In this paper, a numerical investigation on heat transfer performance and flow fields of different nanofluids flows through elliptic annulus in a laminar and turbulent flow regimes. The three-dimensional continuity, Navier–Stokes and energy equations are solved by using finite volume method (FVM) and the SIMPLE algorithm scheme is applied to examine the effects of laminar and turbulent flow on heat transfer characteristics. This study evaluates the effects of four different types of nanoparticles, Al 2 O 3 , CuO, SiO 2 and ZnO, with different volume fractions (0.5–4%) and diameters (25–80 nm) under constant heat flux boundary condition using water as a base fluid were used. The Reynolds number of laminar flow was in the range of 200 ≤ Re ≤ 1500, while for turbulent flow it was in the range of 4000 ≤ Re ≤ 10,000. The results have shown that SiO 2 –water nanofluid has the highest Nusselt number, followed by ZnO–water, CuO–water, Al 2 O 3 –water, and lastly pure water. The Nusselt number for all cases increases with the volume fraction but it decreases with the rise in the diameter of nanoparticles. In all configurations, the Nusselt number increases with Reynolds number. It is found that the glycerine–SiO 2 shows the best heat transfer enhancement compared with other tested base fluids. [ABSTRACT FROM AUTHOR]

This paper addressed new and unique information on the influence of local thermal non-equilibrium (LTNE) effects on heat exchange and entropy generation during thermal-free convection in a non-Darcy porous domain. The simplest configuration was considered, which consisted of a square cavity in which the steady-thermal-free convection motion is generated by maintaining the vertical sidewalls at different and constant temperatures. The Darcy-Brinkman-Forchheimer design has been adopted. The governing equations, which include the two energy equations for the fluid and solid phases, along with momentum equations in their dimensionless form, are solved using the finite volume computational approach. Due to the application of two different heat transport equations under the LTNE modeling technique, sources of entropy generation owing to thermal diffusion in the fluid phase and in the solid phase in addition to the entropy generation owing to viscous dissipation were identified. Maps of the distribution pattern of LTNE sources were also visualized. Furthermore, to assess and compare the thermal diffusion irreversibility in the two components of the porous structure, for the first time, we introduced and examined a new parameter (Ty), which is the ratio of the thermal entropy generation rate in the fluid phase to that in the solid phase. [ABSTRACT FROM AUTHOR]

On course to maximization and optimization of a two-phase closed thermosyphon, this paper expounds on multiple impactful factors in an experimental and numerical setting. Among various fluids, 1-Butanol with 6% concentration, due to having the largest difference in surface tension with water, engendered the most favorable outcome. Response Surface Method has been employed to develop two correlations for efficiency and the thermal resistance of the thermosyphon paving the way for more accurate quantifications without necessarily running costly experiments. Other studied factors based on heat transfer coefficients of evaporator and condenser have been analyzed. The resultant numbers suggest an increase up to roughly 40% and 9% by changing power input and fluid, respectively. Also, enhancements falling within the range of 16 to 20% with the employment of 6% water-Butanol were observed by manipulation of filling ratio. However, coolant mass flow rate influence was limited to less than 10% when exposed to a 40% jump in flow rate if the working fluid was the same, implying its poor dominance in thermal performance of thermosyphon. As 1-Butanol proved superior among enhancing determinants, two numerical cases based on this factor were analyzed, confirming experimental findings while concurrently revealing distinctive phase-change patterns arising from the self-rewetting fluid. • Effect of different self–rewetting fluids on TPCT performance has been investigated. • The 1-Butanol, 1-Pentanol, and 1-Hexanol have been selected as self–rewetting fluids. • Effect of heat input, FR and coolant flow rate on TPCT performance have been studied. • Water/1-Butanol 6% has augmented the h e by 8.6% at 250 W comparing with pure water. • Numerical simulation has been done for water and Water/1-Butanol 6% charged TPCT. [ABSTRACT FROM AUTHOR]

The impingement cooling is used to protect turbine components under high thermal load. This paper conducts a numerical study of heat transfer characteristics of turbine leading edge with lamilloy cooling structure. Target surface curvature and jet-to-surface spacing under various crossflow Reynolds number conditions are considered. Meanwhile, the target surface is dimpled to enhance heat transfer capability. Besides, staggered film holes are considered in the computational domain. The results show that the crossflow induces a counter rotating vortex pair that greatly increase the near wall turbulence and local heat transfer. The vortex pair forms the bound for a U-shaped high heat transfer region caused by the jet impingement. The target surface curvature tends to enlarge the relative area of the U-shaped region. The increased crossflow strength weakens the jet cooling effect, the total heat transfer performance is therefore decreased. Large jet-to-surface spacing enhances the impingement cooling when crossflow is weak but the total heat transfer will not recover as crossflow Reynolds number get higher compared with small and medium spacing cases. • Computational fluid dynamics (CFD) models used to simulate turbine leading edge internal heat transfer. • Impingement cooling configured with dimpled surface and film holes. • Compound influence of jet-to-surface spacing, surface curvature under crossflow. [ABSTRACT FROM AUTHOR]

Hydrofluoroolefins are environment-friendly working fluid and used as replacements for hydrofluorocarbons. A plate heat exchanger with a zeotropic mixture as working fluid has been widely used as a condenser in various thermodynamic systems. However, only very few studies investigated the zeotropic mixture condensation in the plate heat exchanger, and none of these studies addressed mixtures based on hydrofluoroolefins. In this paper, the hydrofluoroolefin mixture condensation in a plate heat exchanger were experimentally tested, and the characteristics of heat transfer and pressure drop were analyzed. We tested the condensation of R1234ze(E)/R1233zd(E) with four different mass fractions at wide ranges of temperatures and flow rates. The test results suggest the R1234ze(E)/R1233zd(E) mixture with the 0.352/0.648 mass fraction presents a 54% maximum degradation in heat transfer coefficient, compared with results obtained using the ideal mixing rule of pure fluids. A modified Silver-Bell-Ghaly model and a pure-fluid correlation can predict the heat transfer and pressure drop data with a mean absolute percentage deviation of 4.1% and 16.1%, respectively. In addition, for the same temperature glide, the heat transfer coefficient and frictional pressure drop of the R1234ze(E)/R1233zd(E) are up to 13.5% and 5.4% higher than those of the R134a/R245fa, respectively. [ABSTRACT FROM AUTHOR]

In this paper transient condensation and heat transfer been investigated on a printed circuit board (PCB) and a surface mounted (SMD) capacitor during a vapour phase reflow soldering (VPS) process. Classic VPS processes provide rapid heating with high heat transfer coefficient rates due to condensation that forms a continuous liquid film on the surfaces. Our aim was to develop a simple and fast computable method that, instead of relying on static descriptions, can reproduce the transient dynamics of the process. It was defined as an inverse heat conduction problem (IHCP) and proposed a solution based on finite difference modelling (FDM) with an alternating direction implicit (ADI) scheme. The layer dynamic was described with a parametric differential equation, and it was coupled to the concentrated and distributed thermal models of the PCB and the capacitor. The parameter values were determined by fitting to measured data. It was found that the heat transfer coefficient is inversely proportional to the layer thickness, and it changes over time according to the dynamic properties of layer growth. It was corroborated that the heat transfer depends on the geometry and thermal properties of the heated surfaces in VPS ovens. The presented method shows good agreement with the validation data. The new method provides a significant update over previous modelling approaches describing the condensation-based heating of the VPS process. [ABSTRACT FROM AUTHOR]

In practice, nanofluids' thermal conductivity and viscosity are the most important parameters in engineering applications. Viscosity affects pumping performance. Theoretical viscosity correlations are widely used in numerical studies. However, existing correlations show an underestimation of the actual viscosity compared to the measurement results. Although many nanofluid viscosity correlations have been developed, there is no generally accepted correlation. This paper reviews the theoretical, numerical, and experimental viscosity correlations and proposes a new correlation based on an analysis of approximately 1200 experimental and 4000 theoretical data tested for about 50 types of nanofluids in the temperature range 273–333 K and particle diameters 2–300 nm. The studied volume fraction range for the nanofluids was up to 10%. Existing correlations take into account the impact of up to two to three parameters The new viscosity correlation is proposed to predict the effective viscosity of nanofluids based on regression analysis of theoretical and experimental viscosity results, and it considers several factors that significantly affect the effective viscosity of nanofluids, such as nanoparticle diameter, density, temperature, types of nanoparticles, and base fluid. [ABSTRACT FROM AUTHOR]

In this paper, the flow behavior in a rectangular channel with miniature riblets (MRs) is numerically investigated. Specially, the MRs are arranged at the bottom of the channel along streamwise direction, and the height of MRs is much less than the thickness of boundary layer. In addition, the heat transfer feature in such a channel is probed as well. The numerical results indicate that the MRs play a role like a "wall" which effectively restrains the momentum exchange of adjacent speed streaks. In addition, it's found that the MRs can regulate the vortices of their surroundings. Furthermore, the flow structure in channel is extracted with the dynamic modal decomposition (DMD), and the frequency of the dominate mode is obtained, which demonstrates the flow stability in channel is improved by the MRs. Therefore, the drag reduction can be achieved consequently. It's also found that the local drag and heat transfer characteristics present similar features with the distance from MRs. Compared with the rectangular channel without MRs, the rectangular channel with MRs shows excellent drag reduction feature, and drag reduction rate is up to 17.19%, which is obtained at the expense of a degree deterioration in heat transfer performance. Furthermore, the comprehensive performance coefficients of various channel with MRs are all less than 1, which illustrates that the MRs is a device that is beneficial to drag reduction but to heat transfer enhancement. • Miniature riblets can restrict the motion of speed streaks in the spanwise. • Streamwise vortex become more orderly for the presence of miniature riblets. • Dynamic mode decomposition is used to show flow stability. • Velocity gradient vector is used to explain the mechanism of drag reduction. • Miniature riblets help to obtain drag reduction but heat transfer improvement. [ABSTRACT FROM AUTHOR]

This paper presents novel treatments for the Ellis non-Newtonian nanofluids flow over a rotating cone in the presence of motile oxytactic microorganisms. These treatments are depending on solutions of the stress tensor equations at specific values of the power-law index α (α = 0,0.5,1, 2) and introducing the stress as expressions in terms of the velocity gradients. Here, four systems of the governing equations for each value of α are presented and the non-similar forms for these systems are obtained. An efficient finite difference method based on the Blottner technique is applied to solve the converted systems. Various important impacts are examined in these simulations such as, magnetic field, non-linear radiation, viscous dissipation, heat generation and Joule heating. Wide ranges of the non-similar parameters are considered, namely, 0 ≤ ξ ≤ 10, 0 ≤ η ≤ 35. The major results revealed that, the skin friction gets higher values at the Ellis case α = 2 while the Newtonian nanofluids α = 1 gives the highest heat transfer rate. Both the velocity and temperature gradients are diminishing as the bioconvection Rayleigh number is enhanced. [ABSTRACT FROM AUTHOR]

This paper presents the flow boiling heat transfer coefficient and pressure gradient measurements of R32 and R1234yf mixtures in a microchannel tube at three concentrations: 15/85, 50/50, and 85/15 by mass. R32/R1234yf mixture has a temperature glide curve that the 15/85 R32/R1234yf mixture has low-temperature glide (0.5 K) while the opposite concentration (85/15) has the highest glide (7 K). The experiment was conducted on a 24-port microchannel tube with an average hydraulic diameter of 0.643 mm. The experiment covers mass flux from 100 to 200 kg-m−2 s−1, heat flux from 0 to 6 kW-m−2, and vapor quality from 0 to 1. Mass flux has a strong effect on both HTC and dP/dz. Heat flux affects HTC but not dP/dz. In addition, the results are compared to pure fluid to discuss the effect of temperature glide. When the glide is higher, the HTC is lower and flatter. At fixed quality, as R1234yf concentration increases, HTC of the mixture decreases slightly first and then increases dramatically. Furthermore, two experiment methods are compared: evaporation in one pass and in one test section. The non-equilibrium in two-phase flow affects concentration gradient in the two phases and further affects the HTC of mixtures with high-temperature glide. • Heat transfer coefficient and pressure gradient of R32/R1234yf are measured. • Three mixtures with different compositions are studied. • Non-equilibrium in two-phase flow affects heat transfer coefficient measurements. • Heat transfer coefficient is lower when the mixture has a larger temperature glide. [ABSTRACT FROM AUTHOR]

A cooling channel model with semi-circular sidewall ribs in a rectangular heat generation body (HGB) is considered in this paper. With fixed volumes of the cooling channel and ribs, constructal design of the cooling channel is implemented with the objective of weighted sum function composed of the heat transfer and flow performances. Multi-objective optimization is further conducted by considering the two performance indexes. The results reveal that the quadratic minimum weighted sum function of the rectangular HGB can be gained by choosing the optimal width-to-height ratio of the cooling channel and the optimal radius of the sidewall ribs. The weighted sum function is augmented by 8.5% after constructal optimization. The comprehensive heat dissipation performance of the rectangular HGB is elevated by employing the suitable number of the sidewall ribs and mass flow rate of the coolant. The smallest deviation index is 0.267, which is gained by the LINMAP decision method, and the corresponding optimal construct can be selected as the design scheme of the cooling channel in a rectangular HGB. Multi-objective optimization provides a Pareto optimal solution set for the comprehensive performance of the rectangular HGB, which provides the heat dissipation designers of various electronic devices with new guidelines. • Constructal design of a cooling channel with semi-circular sidewall ribs in a rectangular heat generation body. • Linear weighted sum of maximum temperature difference and pumping power is minimized. • Multi-objective optimization based on NSGA-II is also conducted and Pareto frontier is obtained. • It provides theoretical guidelines for different design requirements of the electronic devices. [ABSTRACT FROM AUTHOR]

The low energy conversion efficiency of the plasma synthetic jet actuator (PSJA) and the misfiring problem caused by the low gas backfill rate have hindered the application of the PSJA in supersonic aircraft for fast response aerodynamic control. Although the hybrid synthetic jet actuator (HSJA) based on the PSJA has the potential to solve these problems, the heat and mass transfer mechanism of hybrid synthetic jets is still unclear. According to the capacitive discharge process, a novel three-dimensional center energy deposition model was proposed in this paper. The accuracy of the three-dimensional center energy deposition model was verified by comparing it with the experimental results. Considering the damped oscillation of the discharge intensity, the effect of nonconstant center energy deposition on the heat and mass transfer inside the cavity was further discussed. The simulation results show that the electrodes have an impact on the creation and evolution of the vortices inside the cavity. And the three-dimensional nonconstant center energy deposition model reveals the real heat and mass transfer mechanism of the HSJA, which provides the theoretical foundation for improving energy conversion efficiency and gas backfill rate of the HSJA. [ABSTRACT FROM AUTHOR]

Flash evaporation spray is an efficient heat transfer method. Changes in the microstructure and wettability of the cooling surface have important effects on its heat transfer. In this paper, four kinds of cooling surfaces, including a smooth copper surface, a square-column microstructured surface, a superhydrophilic smooth surface, and a superhydrophilic square-column surface, were prepared by chemical corrosion and laser etching. Using liquid nitrogen as the cooling medium, we conducted transient flash evaporation spray experiments on these four types of cooling surfaces. The experimental results show that surface superhydrophilic treatment can substantially enhance the flash evaporation spray of liquid nitrogen. It can more than double the cooling rate for both smooth copper surfaces and square-column microstructured surfaces. In addition, the combination of a microcolumn structure and superhydrophilicity on the cooling surface can provide double reinforcement for the liquid nitrogen flash evaporation spray. Its average cooling rate can reach 131,046 °C/min, and the maximum heat flux is 173 W/cm2. This study sheds some lights on heat transfer mechanism of superhydrophilic microstructure on the flash evaporation spray and contributes to the development of a new method for cell vitrification. [ABSTRACT FROM AUTHOR]

The paper presents a critical review of the performance evaluation criteria (PEC) developed by Webb (Webb, 1981). These criteria evaluate the benefits that could be obtained in heat exchangers if their surfaces and inserts are designed to enhance the heat transfer, particularly in two-fluid heat exchangers in single-phase flow. This study revealed that the imposed constraint for fixed pumping power in the comparison of the augmented channel with the reference one is a major obstacle to achieving greater benefit. Accordingly, the elimination of the constraint of fixed pumping power and the objective of reduced pumping power decreases substantially the criteria of Webb. A new constraint related to the fixed augmentation entropy generation number has been involved replacing the constraint of fixed pumping power. The pumping power can be left to increase until the augmentation entropy generation number is less than unity. The maximum benefit can be obtained when the augmentation entropy generation number reaches the value of unity. The use of greater in tube heat transfer enhancement (with the use of compound heat transfer enhancement techniques instead of simple ones), and with an enhanced outer tube surface of the augmented exchanger is a useful instrument to increase the benefits, only if the augmentation entropy generation number does not cross the frontier of unity. • Enhanced heat transfer surface • Reduction of the performance evaluation criteria • The role of the augmentation entropy generation number • Benefits [ABSTRACT FROM AUTHOR]

The thermal lattice Boltzmann method can be adopted to simulate cavitation bubble collapse in heating or cooling systems. The numerical results satisfy Laplace's law and are consistent with temperature solutions derived from the Rayleigh–Plesset equation. In this paper, in order to study the effects of wall temperature on a collapsing bubble, a calculation model for a cavitation bubble near the heated/cooled wall is established. The influence mechanism of the micro-jet and the cavitation bubble itself on the solid-wall heat transfer, and the thermodynamic behavior characteristics of the cavitation bubble collapse near the wall are obtained. Adjusting the wall temperature T w also affects the thermal effects of cavitation. Furthermore, A dimensionless temperature parameter η is introduced to study the heat transfer intense of the model. The influence of λ , Δ p and R 0 on the heat transfer intense are studied and analyzed. The results show that the optimal λ , Δ p , R 0 and T w values can be used to enhance heat transfer and realize heating or cooling treatment of different surfaces. • Analysis of cavitation bubble in a heating or cooling system is presented by a thermal lattice Boltzmann method. • The influence mechanism of the micro-jet and the cavitation bubble itself on the solid wall heat transfer. • The changes of Tw under different initial wall temperature are analyzed. • A dimensionless parameter η is introduced to study the heat transfer intense, which is related to the λ , Δ p and R 0. • The optimal λ , Δ p , R 0 and T w are used to realize heating or cooling treatment of different surfaces. [ABSTRACT FROM AUTHOR]

In this paper, the effect of an unheated starting length, L 0 varying between 0 and 30 cm, on the burning and heat transfer characteristics over a horizontal Poly (methyl methacrylate) flat plate is experimentally investigated under wind velocities ranging from 0.5–2.0 m/s. The flame images, flame standoff distance, and Nusselt number are measured or calculated. In comparison to the wind velocity, the effect of an unheated starting length is of first-order importance in influencing the flow, heat transfer, and combustion over a solid fuel surface. The unheated segment introduces unique streamwise streaky flames. A critical condition is found to exist at L 0 = 10 cm, where the spanwise wave and lattice structures are observed in the flame, causing the standoff distance and Nusselt number to increase markedly beyond the theoretical prediction. When the unheated segment exceeds a certain length, the increased unheated length effect becomes negligible. Furthermore, the unheated segment shortens the laminar forced convection region and broadens the turbulent buoyant convection region. The study provides very crucial information regarding the effects of an unheated segment on the transitioning mechanism of a wind-driven flame which might be useful and important for fire research. [ABSTRACT FROM AUTHOR]

In this paper, the heat transfer characteristics of a tissue-like capillary porous media are investigated, using the realistic and volume averaging methods. For this purpose, a cylindrical medium is introduced with counter-current vascular network, including longitudinal parallel vessel pairs and numerous interconnect capillaries. The energy equations of solid and fluids phases are derived based on one realistic and two volume averaging methods. Accordingly, the thermal behavior of this capillary porous media was modeled in three cases: constant temperature of solid phase, uniform moderate heat generation in solid phase, and local intensive heat generation in solid phase. The comparison of results for various lengths and densities of interconnect capillaries indicates the inaccuracy of volume averaging method, especially if the supply and return fluids are considered as single integrated phase. Thus, despite much anatomical dissimilarities between the present medium and real living tissues, the occurrences of such errors can be expected if the volume averaging method is used. In addition, the predicted temperature of solid phase at the end of various interstitial heating processes shows that the constant delivery of focused energy in shorter time can increase the maximum temperature of solid phase and its heat affected zone. [ABSTRACT FROM AUTHOR]

In this paper, the finite element method (FEM) and experiment were adopted to evaluate the thermal performance of a multi-chip COB LED lamp based on the cold spray technology. The results show that the junction temperature can be limited under 110 °C. Compared to an aluminum-substrate LED module pressed on the heat sink, the soldering structure of a copper-substrate LED can reduce the junction temperature. The junction temperature of the LED module soldered on the heat sink is only 97.3 °C, while one of the pressing structures is 103.5 °C. It is further found that the chip gaps and the thickness of the copper-circuit layer have significant effect on the heat spread. Increasing the chip gaps and the thickness of the copper-circuit layer can effectively reduce the junction temperature and improve the LED lamp's thermal performance. [ABSTRACT FROM AUTHOR]

Recent works have examined the thermal and dynamical aspects of natural convection occurring in tilted hemispherical cavities whose disk constitutes the hot active wall. The influence of some important aspects on the natural flows have been considered such as the Rayleigh Number, the disk inclination angle with respect to the horizontal plane and the thermal boundary condition on the disk (Dirichlet, Neumann). Combinations of these parameters have been treated in steady state as well as is transient regime. Correlations of Nusselt–Rayleigh type (steady state) and Nusselt–Rayleigh–Fourier type (transient regime) that allow quantifying the heat transfer are proposed in these surveys. The objective of this paper is to synthesize and summarize these works in order to facilitate their implementation in engineering applications. [ABSTRACT FROM AUTHOR]

In the present paper the combination of three-dimensional isothermal and two-dimensional non-isothermal Lattice Boltzmann Method (LBM) are employed to simulate the nucleate pool boiling phenomenon. In order to validate the proposed model, rising bubble phenomenon is simulated afterward the boiling process is investigated by employing a function for heat transfer. The investigation is compared with other numerical works and is found to be in very good agreement. The effects of the parameters including contact angle, heat flux and heater length on departure dimensionless time and departure diameter of bubble are studied. The results show that departure diameter of bubble increases due to the increase of contact angle and decrease of gravity force. Formation, motion and breakup of the bubbles are also investigated as results of gravity force and heat flux. Furthermore, it is worthwhile pointing that out departure diameter of bubble increases as the heat flux increases and increasing of the heater length has more effect in comparison to heat flux on bubble growth. Transient regime is shown by increasing the contact angle and the small bubbles vanishing while rising upward at high gravity force. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical model for studying the effects of shrinkage induced flow on the growth rate of binary alloy dendrites. An equivalent undercooling of the melt is defined in terms of ratio of the phase densities to represent the change in dendrite growth rate due to variation in solutal and thermal transport resulting from shrinkage induced flow. Subsequently, results for dendrite growth rate predicted by the equivalent undercooling model is compared with the corresponding predictions obtained using an enthalpy based numerical method for dendrite growth with shrinkage. The agreement is found to be good. [ABSTRACT FROM AUTHOR]

In this paper, the convective heat transfer of the heat transfer oil-copper oxide nanofluid flow in horizontal smooth and microfin tubes is investigated experimentally. Using a flow control system, the flow regime is always laminar and the wall temperature is constant by using a steam tank. Pure heat transfer oil and nanofluid with the weight concentrations of 0.5%, 1% and 1.5% are used as working fluids. The results are in good agreement with the classic correlations for the pure fluid flow. Based on the results, combination use of nanoparticles and the microfin tube leads to the heat transfer enhancement up to 230%, in comparison with the base fluid flow in the smooth tube. The results are useful in the prediction of the heat transfer rate and the pressure drop in nanofluid flows. [ABSTRACT FROM AUTHOR]

The geometry and heat transfer effects on heat pipes embedded heat sinks-cooling system are investigated in the present paper. In the forced convection system, two different heat pipe geometrical shapes of L and U configurations are taken into account. This study adopts a versatile superposition method and least-square estimators with thermal resistance network analysis to design and experiment their geometry and heat transfer effects under different fan speeds and heat source areas. The results suggest that the characteristics of system performance under varying speeds and areas are significantly different from those under altering speeds and areas. When the thermal performances of these two configurations are 0.04 °C/W of U-shaped heat pipes at 78.85 W, and L-shaped heat pipes are lowest 1.04 °C/W at 34 W, respectively, the lowest thermal resistances of the representative L- and U-shaped heat pipe–heat sink thermal modules are respectively 0.25 °C/W and 0.17 °C/W under twin fans of 3000 RPM and 30 × 30 mm 2 heat sources. The result of this work is a useful thermal management method to facilitate rapid analysis and has provided a useful insight into the design of heat pipe cooling systems. [ABSTRACT FROM AUTHOR]

Thermoelectric systems (TE) can directly convert heat to electricity and vice-versa by using semiconductor materials. Therefore, coupling between heat transfer and electric field potential is important to predict the performance of thermoelectric generator (TEG) systems. This paper develops a general two-dimensional numerical model of a TEG system using nanostructured thermoelectric semiconductor materials. A TEG with p-type nanostructured material of Bismuth Antimony Telluride (BiSbTe) and n-type Bismuth Telluride (Bi2Te3) with 0.1 vol.% Silicon Carbide (SiC) nanoparticles is considered for performance evaluations. Coupled TE equations with temperature dependant transport properties are used after incorporating Fourier heat conduction, Joule heating, Seebeck effect, Peltier effect, and Thomson effect. The effects of temperature difference between the hot and cold junctions and surface to surrounding convective on different output parameters (e.g., thermal and electric fields, power generation, thermal efficiency, and current) are studied. Selected results obtained from current numerical analysis are compared with the results obtained from analytical model available in the literature. There is a good agreement between the numerical and analytical results. The numerical results show that as temperature difference increases output power and amount of current generated increase. Moreover, it is quite apparent that convective boundary condition deteriorates the performance of TEG. [ABSTRACT FROM AUTHOR]

This paper presents a numerical analysis of a steady three-dimensional fluid flow and heat transfer towards a permeable shrinking sheet. The governing nonlinear partial differential equations are transformed into a system of ordinary differential equations by a similarity transformation, which are then solved numerically by a shooting method. The effects of the governing parameters on the skin friction and heat transfer from the surface of the shrinking surface are illustrated graphically. It is found that dual solutions exist for the shrinking case. A comparison with known results from the open literature has been done and it is shown to be in excellent agreement. [ABSTRACT FROM AUTHOR]

It is significant to develop an expression for the rarefaction correction to the continuum solution for heat transfer. An extended Reynolds analogy for slip and transition flow heat transfer in microchannels and nanochannels is proposed. A relationship between the rate of the dimensionless mean wall shear stress reduction and the rate of the dimensionless mean wall heat flux reduction may exist. The extended Reynolds analogy can be utilized to obtain an initial engineering approximation of the Nusselt number. As slip flow heat transfer is inherently complex, the proposed simple model may provide an insight into the mechanism of slip flow heat transfer. This paper cultivates the facility to perform the kind of engineering analysis which, although not exact, still provides useful information concerning real engineering needs. [ABSTRACT FROM AUTHOR]

In this paper, a set of new data is proposed for the simultaneous reconstruction of thermal radiation and conduction properties in a radiation-conduction medium into the one-dimensional layer. The radiation problem is modeled by the modified discrete ordinates method, and the conduction-radiation heat transfer problem is solved via the finite volume approach. The inverse problem is solved using the particle swarm optimization algorithm. Various cases are solved in this paper. In the first section, the constant absorption coefficient and radiation-conduction parameters are reconstructed by measuring the exit radiation intensities. To increase the accuracy of results, a two-stage hybrid optimization algorithm is used in this section. In the first stage, the absorption coefficient is calculated, and in the second stage, the radiation-conduction parameter is obtained. In the second section, the ability of the proposed algorithm and the measured data for reconstruction of the temperature-dependent radiation-conduction parameter is tested. To improve the results' accuracy in this section, a set of new data is used. Consequently, the proposed algorithm with a modified objective function that uses new data is presented to decrease the Planck number's sensitivity to the measurement errors. [ABSTRACT FROM AUTHOR]

The mini-diameter loop thermosyphon, which has an excellent heat transfer performance with simple, compact structure and pump-free advantages, can effectively solve the problem of heat transfer under high heat load in a confined space. The mini-diameter loop thermosyphon exhibits different gas-liquid transport and heat transfer patterns than the conventional-diameter one due to various gas-liquid phase transformation properties and a strong friction force in the mini-diameter channel. Furthermore, data on the visual analysis of gas-liquid transport and heat transfer properties of the mini-diameter loop thermosyphon under various filling ratios is still lacking. In this paper, a visible experimental research on a mini-diameter loop thermosyphon (3 mm) in a wide filling ratio range(44% -97%) is undertaken. The maximal heat transfer capacity increases initially and subsequently falls with the filling ratio, according to the testing data. At a low filling ratio, the flow pattern changes as slug flow - churn flow - annular flow with the heat load increase, leading to a low loop thermal resistance, and dry out occurs at 185 W heat load under 50% filling ratio. The gas-liquid flow shifts to slug flow-geyser boiling-bubble flow at high filling ratios (73% and 82%), and the bubble departure diameter steadily decreases with increasing heat load. Consequently, the heat transfer performance (thermal resistance) has been enhanced, and the maximum heat transfer capacity has been increased to 280 W. Single-phase flow is plainly seen in the loop when the filling ratio reaches 91% or even 97%, thus reduced heat transfer capacity. Therefore, the high-filling-ratio mini-diameter loop thermosyphon is better for high-load heat dissipation. However, a low thermal resistance shows at the low filling ratio, but the heat load is also low. As a result, a loop thermosyphon with a low filling ratio should be selected for the low heat load situation. [ABSTRACT FROM AUTHOR]

Synthesizing stable nanofluids with favourable thermal properties that can cater to practical applications is a challenge over the past few years. This paper presents the preparation and analyzes the thermal efficiency of the novel nanofluid prepared by the suspension of nanocrystalline Cr 2 AlC MAX phase powder in ethylene glycol (EG). Incorporation of h-BN , MoS 2 , Al 2 O 3 , and Cr 2 AlC showed a thermal conductivity enhancement at 303 K when compared to EG. Accurate experimental models for the thermal conductivity and the viscosity of EG + Cr 2 AlC nanofluids are estimated. The theoretical analysis of the flow profiles of EG + Cr 2 AlC/Al 2 O 3 /MoS 2 /h-BN nanofluids is carried out with Blasius and Sakiadis flow models. The Cr 2 AlC MAX phase possesses both ceramic and metal properties that help these nanofluids to show high heat transfer performance. The results show that 0.50 wt% EG + Cr 2 AlC nanofluid displays maximum improvement in heat transfer performance. There is a substantial rise in the thermal conductivity when both temperature and weight fraction increase. The simulated flow of the nanofluid past a plate indicated superior heat transfer and thermal profiles for the EG + Cr 2 AlC nanofluids. For the flow past a moving plate, the nanofluid possesses less skin friction at the plate, which is favourable for various practical applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Supercritical CO 2 (sCO 2) is considered as an ideal heat transfer fluid for power cycles adapted to a wide range of heat sources. This paper employs computational approach based on Reynolds-Averaged Navier-Stokes (RNAS) modelling to study highly buoyant turbulent sCO 2 flow and heat transfer heated in various horizontal tubes with diameter of 4.57 mm, 13.39 mm, and 22.14 mm. The conditions with relatively high ratio of heat flux q to mass flux G are simulated. The chosen AKN k − ε low-Reynolds number turbulence model is rigorously validated against experiments and DNS covering a wide range of operation conditions and exhibits quite satisfactory consistencies on the strong buoyancy reproductions of horizontal supercritical flows. With sCO 2 heat transfer data presented, details about the coupled turbulent flow characteristics have been discussed. It has been observed that in various size horizontal geometries, not only the local sCO 2 heat transfer along the tube top surface, but also the overall performance within the liquid-like region near T pc is greatly degraded by the strong buoyancy, and the deterioration regime expands with decreasing pipe diameter. For the highly buoyant horizontal sCO 2 flows, a backflow vortex appears near the top wall then a second velocity peak forms which locates further into the core flow section for larger diameter pipes; The radial velocity profile of the top wall has been flattened even distorted into "half-M" shape that the turbulence statistics decline remarkably then the turbulent activities and thermal advection are attenuated. With sCO 2 heated into the gas-like regime, the heat transfer recovers because of the reduced buoyancy effects. • Highly buoyant turbulent sCO 2 flow and heat transfer heated in various horizontal tubes are investigated. • AKN k − ε turbulence model is rigorously validated to exhibit good ability on strong buoyancy reproduction. • In-depth analysis has been performed on the coupled turbulent flow and heat transfer behaviours of horizontal sCO 2. • Influences of the horizontal pipe diameter are discussed. [ABSTRACT FROM AUTHOR]

In this paper, laminar natural convection heat transfer was numerically investigated in cubical air-filled enclosures with partitions attached to the walls with different positions. Steady-state governing equations were solved using the Boussinesq approximation by the finite volume method. Two cases were considered that the partitions were placed perpendicular (Case 1) and parallel (Case 2) to the active walls, respectively. The opposing lateral walls of the enclosure are heated and cooled while the other walls are adiabatic. The effect of the two inclined partitions attached to the bottom and top adiabatic walls at the different positions on the heat transfer rate was examined. The dimensionless partition heights and positions were h/H = 0.1, 0.2 and 0.3, and c/H = 0.25, 0.5 and 0.75, respectively. The inclination of the partitions was θ =3°, 4°, and 5°. The air (Pr = 0.7) streamlines and the temperature fields were obtained for the Rayleigh numbers 103 ≤ Ra ≤ 106 for both cases studied. The mean dimensionless heat transfer ratio (Nusselt number) over the cold wall for both cases was also obtained. The effects of the dimensionless parameters considered on the heat transfer for both cases were concluded. It was seen that the parameters considered are important for Case 2 whereas they did not play a major role for Case 1. • The effect of dual partitions on the laminar natural convection in a cubical enclosure was investigated. • The parameters are the dimensionless heights, positions and inclinations of the partitions. • Novel correlations are derived for the cubical enclosure with dual partitions. [ABSTRACT FROM AUTHOR]

The microscale heat transport equation (MHTE) is an important model in the microtechnology. The MHTE differs from the classical model of heat diffusion since it includes temperatures derivatives of second- and third-order with respect to time, and space and time, respectively. This paper studies the application of the localized radial basis function partition of unity (LRBF-PU) method for finding the MHTE solution. The proposed algorithm discretizes the unknown solution in two phases. First, the discretization of time dimension is obtained through the finite difference with second order accuracy. In addition, the unconditional stability and the convergence of the temporal semi-discretization are analysed with the help of the discrete energy method in an appropriate Sobolev space. Second, the discretization of the spatial dimension is accomplished with the help of the LRBF-PU. One of the main disadvantages of global collocation techniques is the high computational cost caused by the associated dense algebraic system. Using the proposed strategy, one can divide the original domain into a number of sub-domains through a kernel approximation over every sub-domain. The LRBF-PU method avoids the ill-conditioning driven by global collocation RBF-based methods and decreases the related computational cost. Numerical examples highlight the robustness and accuracy of the LRBF-PU. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to study the turbulent flow of pseudo-plastic nanofluids (PPNF) and heat transfer subject to wall slip. Four types of nanoparticles (Fe 3 O 4 , CuO, Cu, Ag) are taken into account in carboxymethyl cellulose (CMC)-water-based fluid. The Prandtl mixing length theory is introduced to divide the turbulent boundary layer into two regions: laminar sub-layer and turbulent region. The numerical solutions are obtained by bvp4c technique. Results show that the wall-slip parameter has important influence on velocity and temperature fields, the variations are more intensive in laminar sub-layer. The local friction coefficient decreases for larger wall-slip parameter and smaller fraction of nanoparticles. And the heat transfer is significantly strengthened (in Nusselt number) for smaller wall-slip parameter and larger fraction of nanoparticles. Moreover, for four different nanofluids, the Ag/CMC nanofluid is more conducive to enhance the turbulent heat transfer than other nanofluids. • An approach on turbulent flow and heat transfer of pseudo-plastic nanofluids plate with wall slip are presented. • Prandtl mixing length theory is introduced and numerical solutions are obtained by bvp4c technique. • Results show wall-slip and volume fraction have important influence on velocity and temperature fields. • Local friction coefficient decreases for larger wall-slip parameter and smaller volume fraction. • Heat transfer are significantly strengthened for smaller wall-slip parameter and larger volume fraction. [ABSTRACT FROM AUTHOR]

In current context, applying multi tapes were recommended as promising technique for augmentation cross section flow. Type of carrier fluid was changed with adding copper oxide nano powders with fraction of 0.04. Residence time improves with applying tapes and nanoparticles pass longer path inside the pipe. Gravity has no impact in momentum equation due to high velocity and owing to presence swirl flow device; k-ɛ technique was applied. For verification, empirical formula for estimating Nu was involved. Recirculation zone augment as b increases and stronger secondary flow generates thinner layer near the surface and make it cooler. Greater pressure loss is an output of more interaction of nanomaterial with solid surfaces and this phenomenon occurs in existence of tapes. Owing to longer paths of nano particles, pressure loss augments with growth of b and Re. Cooling rate enhances about 3.77% and 128.9% with rise of b and Re. Growth of Re enhances the increasing trend of S gen,f. This function augments about 64.41% with rise of b at highest Re. Also, growth of b leads to reduction in S gen,th about 3.09%. [ABSTRACT FROM AUTHOR]

Abstract: Enhancing heat transfer mechanisms are used in many industrial applications like heat exchanger, air conditioning, chemical reactors and refrigeration systems. Therefore several techniques have been promoted to enhance heat transfer rate and to decrease the size and cost of equipment especially the heat exchangers. One of the leading tools used in passive heat transfer methods mainly at turbulence flow is twisted tape inserts. The current paper acclaims that want to review experimental researches done on this technique in recent years at the turbulent zone and with respect to the overall enhancement ratio pick the most efficient type of twisted tape. [Copyright &y& Elsevier]

Abstract: In this paper an experimental study of convective boiling heat transfer of R-600a/oil/nanoparticle mixtures is investigated. The experimental setup was prepared with a smooth horizontal tube as a test section with the length and diameter of 9.5 and 103mm, respectively, and pure R-600a was applied for evaluating the heat transfer enhancement. Six mixtures containing 1% weight fraction of R-600a/oil with different concentrations of CuO nanoparticles including 0.0, 0.5, 1.0, 1.5, 2.0 and 5.0% weight fraction of R-600a/oil/nanoparticle were used in our study. The mass velocity per cross area was considered at the range of 50–700kg/m2 s for low vapor quality (ϕ <0.25). The results showed that the convective boiling heat transfer coefficient will be increased by increasing the mass fraction of nanoparticles up to 2%, while by increasing the mass fraction of nanoparticles up to 5% the heat transfer coefficient will be reduced. [Copyright &y& Elsevier]

Abstract: The purpose of this paper was to present an inverse heat conduction method used for determining the local convective boiling heat transfer coefficient in mini-channel for pure water, copper nanofluid by using three different concentrations of nanoparticles: 5mg/L, 10mg/L and 50mg/L. Conjugated gradient method with adjoint equation is used to solve the IHCP and estimate directly the space-variable convective heat transfer coefficient. Direct estimation local convective boiling heat transfer coefficient is a nonlinear inverse heat problem. The uncertainties in the estimated in heat transfer coefficient are calculated using bias and variance errors. This method is able to estimate local convective boiling heat transfer coefficient very well. [Copyright &y& Elsevier]

It has been reported that the benefit of ultrasonic enhancement on saturated boiling heat transfer is limited. This paper studies the synergistic effects of tube structure and ultrasound on saturated boiling heat transfer. Three tubes are analyzed: a smooth tube, a two-dimensional finned tube and a three-dimensional finned tube. It is found the ultrasound enhancement ratios of the three tube types decrease with increasing ultrasonic power and are smaller under a 45 kHz ultrasonic frequency than a 21 kHz ultrasonic frequency. Ultrasound hinders the saturated boiling heat transfer of the smooth tube and the two-dimensional finned tube under nearly all the experimental conditions in this paper. When the ultrasonic frequency is 21 kHz, the ultrasound enhancement ratio of the three-dimensional finned tube is below zero at low heat flux but above zero at large heat flux. The three-dimensional structure of the tube contributes to the improved heat transfer behavior in two ways. First, the interface interaction between wall and bubbles is smaller. Second, the ultrasound propagating along the intersected grooves produces a vortex flow of the liquid, and the resulting stronger stretching and contracting of the bubbles promote heat transfer performance. [ABSTRACT FROM AUTHOR]

The focus of this study is to see how nanoparticle shape affects, mixed convective flow along a vertical impermeable wall in a non-Darcy porous medium. The temperature maintained at the wall is constant and the ambient temperature is far from the wall. The two different nanoparticles Fe 3 O 4 (Ferrous) and Al 2 O 3 (Non Ferrous) as well as the water is taken as a base fluid. The two different shapes of nanoparticles considered here are blade and brick. The partial differential equations are solved numerically using the shooting technique employing local similarity transformations. Between the previously published paper and the current findings, there is a favourable correlation. Graphically depicted are the impacts of various nanoparticles and their shapes on velocity, temperature, and heat transfer. It has been discovered that blade shaped nanoparticles have a higher velocity than brick shaped particles. As a comparison of heat transfer in Darcy and non-Darcy flows for different volume fractions is investigated. [ABSTRACT FROM AUTHOR]

The paper presents investigation results on heat transfer in falling films of refrigerant R21 on an array of horizontal tubes with a coating deposited by the method of microarc oxidation (MAO). Different MAO-coatings were applied on the surface of tubes of aluminum alloys AD31 and D16T with a diameter of 10 mm in silicate-alkaline, acidic, and phosphate electrolytes. Two coated test tubes were copper-plated additionally in a copper sulfate solution. The enhancement of heat transfer on the tubes with a porous coating depends in a complex manner on the parameters of MAO-coating surfaces defined by their treatment regimes. The highest 3-fold heat transfer enhancement in comparison with plain tube in the nucleate boiling regime was achieved on the surface of a tube made of alloy D16T with the MAO coating of 30-μm thickness, obtained in a silicate-alkaline electrolyte. Additional deposition of copper particles on the MAO-coatings leads to an enhancement of heat transfer by (20–30) % compared to plain tube. In the studied range of Reynolds number 600–1500, the effect of irrigation density on the heat transfer coefficients is not observed. [ABSTRACT FROM AUTHOR]

Ultrasound, as the considerable field energy source, has a significant effect on heat transfer enhancement. Although there has been deeply researched on the utilization of ultrasound in heat exchangers, the ambient environment conditions are usually ignored. In this paper, controlling vibratory surface by user defined function, the heat transfer enhancement induced by ultrasound is numerically studied in immersed coil heat exchangers, and effects of acoustic intensity, ambient pressure and ambient fluid flow velocity on the heat transfer enhancement are investigated. The results show the heat transfer enhancement factor η h reaches to 24.26% after ultrasonic treatment for 0.005 s. When the vibratory amplitude increases from 20 μm to 35 μm, η h raises from 15.67% to 26.71%. With an increase of the ambient pressure from 0.1 MPa to 1.0 MPa, η h changes from 24.26% to 48.43%. While the inlet flow velocity decreases from 1.0 m/s to 0.1 m/s, η h varies from 1.76% to 39.01%. This research based on immersed coil heat exchangers has evaluated the influence of acoustic intensity and ambient fluid properties on acoustic streaming and acoustic cavitation, which provides with a guidance in the utilization of ultrasound in heat exchangers. • The heat transfer of immersed heat exchangers is promoted by acoustic phenomena. • Higher ultrasound amplitude will bring better heat transfer enhancement effect. • Ambient pressure increasement causes ultrasound power consumption increases exponentially. • Ultrasound performance is more effective under lower ambient fluid velocity. [ABSTRACT FROM AUTHOR]